Word Viewer
Word Viewer is a free Microsoft application that allows you to open and read Microsoft Word documents.
Perhaps you don't have Microsoft Office currently installed. One day down the road you may be sent a Microsoft Word file or two. You may find that you don't need to make any edits, you just need to view the file. Then this is the program to have in your arsenal, and it's worth bookmarking - or better yet - installing.
Microsoft understands that their Word Document format is a highly-used standard, but doesn't want to require you to have to buy the whole program just to open one file when someone sends one to you. So, if you have Microsoft Word installed, you should at least have Word Viewer ready. It will do a better job at properly opening Word files (with all the specific document formatting) than any built-in email Word Viewer or competing Word-compatible program. The latest version of Word Viewer is compatible with those pesky .docx files.